Devices, systems, and methods for determining linear and angular accelerations of the head

ABSTRACT

Mouth guards and related systems and methods for determining linear and angular accelerations of the head of a subject. A plurality of accelerometers are operatively associated with the mouth guard and spaced from one another about the mouth guard. The accelerometers produce outputs indicative of the linear and angular acceleration of the mouth guard. Optionally, the mouth guard can be used in conjunction with a helmet that is provided with a plurality of accelerometers spaced about the helmet. In use, the outputs of the accelerometers of the helmet can be correlated to the outputs of the accelerometers of the mouth guard.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of the filing date of U.S.Provisional Patent Application No. 61/747,411, filed Dec. 31, 2012,which is incorporated herein by reference in its entirety.

FIELD

This application relates to devices, systems, and methods for measuringand/or determining the linear and angular acceleration experienced bythe head of a subject in response to an impact force.

BACKGROUND

The human brain is susceptible to injury due to both linear and angularacceleration. Linear and angular acceleration above the threshold and/orother linear and angular acceleration characteristics, such as the timederivative of the acceleration (known as “the jerk”), that could causebrain injury can occur in athletes participating in sports, such assoccer, boxing, skiing, snowboarding, hockey, American football,motorcycle and automobile racing, and bicycling, and to soldiers whoexperience an explosive blast or other impact.

Accordingly, there is a need in the pertinent art for devices, systems,and methods for measuring both linear and angular acceleration of thehead of a subject.

SUMMARY

Described herein is a mouth guard for determining the linear and angularacceleration of the head of a subject. The mouth guard can include aU-shaped element having an outer side wall, an inner side wall, and atleast one biting surface. The outer side wall, the inner side wall, andthe at least one biting surface can cooperate to define at least onechannel configured to receive the upper teeth of the subject. The mouthguard can also include a plurality of accelerometers operativelyassociated with the U-shaped element. The plurality of accelerometerscan be spaced from one another about the U-shaped element. Eachaccelerometer of the plurality of accelerometers can be configured toproduce an output indicative of the linear and angular acceleration ofthe mouth guard.

The mouth guard can be provided as part of a system. Such a system caninclude processing circuitry positioned in operative communication withthe plurality of accelerometers of the mouth guard. The processingcircuitry can be configured to receive the outputs from the plurality ofaccelerometers of the mouth guard.

Also described herein is a helmet having a wall that defines an innerchamber. The inner chamber can be configured to receive the head of thesubject. The helmet can include a plurality of accelerometersoperatively associated with the wall of the helmet. The plurality ofaccelerometers can be spaced from one another about the helmet. Eachaccelerometer of the plurality of accelerometers of the helmet can beconfigured to produce an output indicative of the linear accelerationand angular acceleration of the helmet.

The helmet can also be provided as part of a system. Such a system caninclude processing circuitry positioned in operative communication withthe plurality of accelerometers of the helmet. The processing circuitrycan be configured to receive the outputs from the plurality ofaccelerometers. The processing circuitry can be further configured toconvert the outputs from the plurality of accelerometers of the helmetinto an output indicative of the linear and angular acceleration of thehead of the subject.

In use, the head of the subject can be positioned within the helmet, andthe mouth guard can be positioned in engagement with the upper teeth ofthe subject. In response to the delivery of a first impact force to thehelmet, each accelerometer of the helmet can be configured to produce anoutput indicative of the linear and angular acceleration of the helmet,and each accelerometer of the mouth guard can be configured to producean output indicative of the linear and angular acceleration of the mouthguard (which substantially corresponds to the linear and angularacceleration of the head of the subject). The outputs of theaccelerometers of the helmet and the mouth guard can be transmitted tothe processing circuitry. The processing circuitry can determine atransfer function configured to convert the outputs of theaccelerometers of the helmet (linear and angular accelerations of thehelmet) to the outputs of the accelerometers of the mouth guard (linearand angular accelerations of the mouth guard).

After the transfer function has been determined, the mouth guard can bedisengaged from the teeth of the subject and removed from the mouth ofthe subject. Following removal of the mouth guard, a second impact forcecan be delivered to the helmet. In response to delivery of the secondimpact force, each accelerometer of the helmet can be configured toproduce an output indicative of the linear and angular acceleration ofthe helmet. The outputs of the accelerometers of the helmet can then betransmitted to the processing circuitry. The processing circuitry canthen apply the transfer function to the outputs of the accelerometers ofthe helmet to determine the linear and angular acceleration of the headof the subject.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features of the preferred embodiments of the inventionwill become more apparent in the detailed description in which referenceis made to the appended drawings wherein:

FIG. 1A is a schematic diagram of a measurement system comprising amouth guard and processing circuitry as disclosed herein. FIG. 1B is aperspective view of an exemplary mouth guard as disclosed herein. FIG.1C is a schematic diagram of a measurement system comprising a helmetand processing circuitry as disclosed herein.

FIG. 2 depicts an exemplary local mouth guard coordinate system havingaxes x, y, and z and origin O. In the exemplary mouth guard system shownin FIG. 2, three 2-axis accelerometers (a total of six accelerometers tomeasure linear acceleration in the directions shown by the arrowsoriginating from the respective accelerometers) are positioned andoriented in the mouth guard for accurate and precise determination ofthe angular and linear accelerations of the mouth guard origin O, markedby the arrows originating from point O.

FIG. 3 depicts an exemplary local mouth guard coordinate system havingaxes x, y, and z and origin O relative to the head coordinate systemaxes u, v, and w and origin and center of mass G. The accelerations ofthe head center of mass are indicated by the arrows originating frompoint G.

FIGS. 4-5B display an experimental setup that was used to investigatethe accelerations of the head during soccer ball heading. Theaccelerations were measured using an exemplary accelerometer chipoperatively associated with a mouth guard as disclosed herein.

FIGS. 6-8 display the experimental acceleration data that were measuredusing the experimental setup of FIGS. 4-5B. In FIGS. 6-8, the x and ydirections correspond with the chip x and y directions shown in FIG. 5A,where x is the head forward direction and y is the head upwarddirection.

FIGS. 9-10 and 12 display an experimental setup that was used to measureaccelerations of the head resulting from impact forces that occur duringsoccer ball heading. In FIG. 10, the head coordinate system axes aredenoted by x, y, and z, corresponding with the head front, left, and updirections and with the x, y, and z coordinate system origin at the headcenter of mass.

FIGS. 11 and 13-18 display the experimental force and acceleration datathat were measured using the experimental setup of FIGS. 9-10. The forceand impulse data shown in FIGS. 13 and 14 were derived fromframe-by-frame analysis of high-speed video. A representative frame ofthe high-speed video is depicted in FIG. 12. The acceleration data shownin FIGS. 11 and 15-18 were derived from the output of the mouth guardshown in FIG. 9. In FIGS. 15 and 16, the head coordinate system axes aredenoted by x, y, and z, corresponding with the head front, left, and updirections and with the x, y, and z coordinate system origin at the headcenter of mass.

FIG. 19 shows the fitting of a bridge element to three-dimensional scansof the (A) upper jaw and (B) upper and lower jaws of a subject asdisclosed herein.

FIG. 20 depicts a solid model of a fitted bridge element as disclosedherein.

FIG. 21 displays an image of a bridge element printed using athree-dimensional printer.

FIG. 22 displays an exemplary thermoplastic mouth guard with a bridgeelement, two PCB assemblies (each having two accelerometers), wiring,and sealant. A third PCB (having two accelerometers) is hidden from viewon the left side of the mouth guard bridge element.

FIG. 23 displays an alternative configuration of the mouth guard of FIG.22.

FIG. 24 depicts the use of biometric markers to determine the linear andangular positioning of a mouth guard relative to the head of a subjectas disclosed herein.

FIG. 25 depicts a graph of peak force of a ball on the head of a subjectversus the relative ball velocity, as determined by high-speed-videoframe-by-frame analysis as disclosed herein.

FIG. 26 depicts a graph of the peak magnitude of linear acceleration ofthe head center of mass of a subject in the saggital (xz) plane versusthe relative ball velocity, as measured by an exemplary mouth guard asdisclosed herein. In FIG. 26, the head coordinate system axes aredenoted by x, y, and z, corresponding with the head front, left, and updirections and with the x, y, and z coordinate system origin at the headcenter of mass.

FIG. 27 depicts a graph of the angular acceleration of the head of asubject about the y-axis versus the relative ball velocity, as measuredby an exemplary mouth guard as disclosed herein. In FIG. 27, the headcoordinate system axes are denoted by x, y, and z, corresponding withthe head front, left, and up directions and with the x, y, and zcoordinate system origin at the head center of mass.

DETAILED DESCRIPTION

The present invention can be understood more readily by reference to thefollowing detailed description, examples, drawings, and claims, andtheir previous and following description. However, before the presentdevices, systems, and/or methods are disclosed and described, it is tobe understood that this invention is not limited to the specificdevices, systems, and/or methods disclosed unless otherwise specified,and, as such, can, of course, vary. It is also to be understood that theterminology used herein is for the purpose of describing particularaspects only and is not intended to be limiting.

The following description of the invention is provided as an enablingteaching of the invention in its best, currently known embodiment. Tothis end, those skilled in the relevant art will recognize andappreciate that many changes can be made to the various aspects of theinvention described herein, while still obtaining the beneficial resultsof the present invention. It will also be apparent that some of thedesired benefits of the present invention can be obtained by selectingsome of the features of the present invention without utilizing otherfeatures. Accordingly, those who work in the art will recognize thatmany modifications and adaptations to the present invention are possibleand can even be desirable in certain circumstances and are a part of thepresent invention. Thus, the following description is provided asillustrative of the principles of the present invention and not inlimitation thereof.

As used throughout, the singular forms “a,” “an” and “the” includeplural referents unless the context clearly dictates otherwise. Thus,for example, reference to “an accelerometer” can include two or moresuch accelerometers unless the context indicates otherwise.

Ranges can be expressed herein as from “about” one particular value,and/or to “about” another particular value. When such a range isexpressed, another aspect includes from the one particular value and/orto the other particular value. Similarly, when values are expressed asapproximations, by use of the antecedent “about,” it will be understoodthat the particular value forms another aspect. It will be furtherunderstood that the endpoints of each of the ranges are significant bothin relation to the other endpoint, and independently of the otherendpoint.

As used herein, the terms “optional” or “optionally” mean that thesubsequently described event or circumstance may or may not occur, andthat the description includes instances where said event or circumstanceoccurs and instances where it does not.

The word “or” as used herein means any one member of a particular listand also includes any combination of members of that list.

Described herein with reference to FIGS. 1-27 are devices, systems, andmethods for determining the linear and angular acceleration of the headof a subject. It is contemplated that the subject can be a human ornon-human subject. It is further contemplated that the subject can havea head, a mouth, and upper and lower teeth.

The Mouth Guard

In exemplary aspects, and with reference to FIGS. 1A-1C, a mouth guard10 can be provided for engagement with the teeth of the subject. Inthese aspects, it is contemplated that the mouth guard 10 can comprise aU-shaped element 12 having an outer side wall 14, an inner side wall 16,and at least one biting surface 18. It is further contemplated that theouter side wall 14, the inner side wall 16, and the at least one bitingsurface 18 can cooperate to define at least one channel 20 configured toreceive the upper teeth of the subject. In exemplary aspects, thechannel 20 can be shaped to conform to the upper teeth of the subject.In these aspects, the channel 20 can be formed from a mold of the upperteeth of the subject. It is contemplated that a good fit between themouth guard 10 and the upper teeth and gums of the subject can create avacuum seal that prevents the mouth guard from being loose and rattlingagainst the teeth during head impacts. In use, it is contemplated thatthe mouth guard 10 can be tightly fitted to the upper teeth and gums andbe configured for relatively loose engagement with the lower teeth ofthe subject.

In one aspect, the mouth guard 10 can comprise a plurality ofaccelerometers 30 operatively associated with the U-shaped element 12.In this aspect, it is contemplated that the plurality of accelerometers30 can be spaced from one another about the U-shaped element 12. It isfurther contemplated that each accelerometer 30 of the plurality ofaccelerometers of the mouth guard 10 can be configured to produce anoutput indicative of the linear and angular acceleration of the mouthguard.

In another aspect, the plurality of accelerometers 30 of the mouth guard10 can optionally comprise nine single-axis accelerometers (capable ofmeasuring linear acceleration in a single axis) positioned at threedistinct locations about the U-shaped element 12, as shown in FIGS. 1Band 2. In this aspect, three orthogonal single-axis accelerometers canbe positioned in a cluster at each of the three distinct locations.Alternatively, the plurality of accelerometers 30 of the mouth guard 10can comprise three three-axis accelerometers (capable of measuringlinear acceleration in three axes), with one accelerometer positioned ateach of the three distinct locations. In exemplary aspects, when theplurality of accelerometers are positioned at three distinct locationsand positioned and oriented within a common plane (for example andwithout limitation, within the xy plane) as shown in FIGS. 1B and 2, itis contemplated that the plurality of accelerometers can comprise threetwo-axis accelerometers, with one two-axis accelerometer positioned ateach of the three distinct locations. In further exemplary aspects, whenthe plurality of accelerometers are positioned at three distinctlocations and positioned and oriented within a common plane as shown inFIGS. 1B and 2, it is contemplated that the plurality of accelerometerscan comprise six single-axis accelerometers, with a cluster of twosingle-axis accelerometers being positioned at each of the threedistinct locations.

In exemplary aspects, the three distinct locations can correspond tofirst, second, and third locations spaced from one another about an arcdefined by the U-shaped element 12. In these aspects, it is contemplatedthat the U-shaped element 12 can define opposed first and second ends22, 24. It is further contemplated that the U-shaped element 12 can besubstantially symmetrical about a central axis 26, which can optionallycorrespond to a y-axis as disclosed herein. In exemplary aspects, it iscontemplated that the first location can be proximate the first end 22of the U-shaped element 12, the second location can be proximate thesecond end 24 of the U-shaped element, and the central axis 26 canintersect the third location. Thus, it is contemplated that the threedistinct locations at which the plurality of accelerometers arepositioned can correspond to: (1) a position just outside the rightmolars of the subject; (2) a position just outside the left molars ofthe subject; and (3) a position just in front of the central incisors ofthe subject.

Although described herein as being positioned at three distinctlocations within the mouth of the subject, it is contemplated that otherpositions and orientations of the plurality of accelerometers 30 can beemployed to determine the linear and angular accelerations of the headof the subject. It is further contemplated that the plurality ofaccelerometers 30 can comprise any number of accelerometers that providesufficient data to determine the linear and angular accelerations of thehead of the subject. For example, it is contemplated that the pluralityof accelerometers 30 can comprise more than nine accelerometers.

The majority of head impacts have a small duration (often a fewthousandths of a second or less) and large angular accelerations. It iscontemplated that, although gyroscopes are typically used to determineangular accelerations and velocities and positions, conventionalgyroscopes cannot be used to measure many of the short-duration impactsthat generate large angular accelerations of the head of the subject.Nonetheless, in appropriate conditions, it is contemplated that one ormore gyroscopes can be used in place of one or more of theaccelerometers of the plurality of accelerometers to determine thelinear and angular accelerations of the head of the subject.

In exemplary aspects, the plurality of accelerometers 30 of the mouthguard can comprise microelectromechanical system (MEMS) accelerometers.In these aspects, it is contemplated that the MEMS accelerometers can beconfigured to measure large accelerations at relatively high acquisitionrates while being small enough in mass to not significantly affect theinertia on the head of the subject. It is further contemplated that theMEMS accelerometers can be provided on a chip.

In other exemplary aspects, the disclosed mouth guard 10 can optionallycomprise one or more hard thermoplastic materials. In these aspects, itis contemplated that the one or more hard thermoplastic materials can beheated and vacuum-formed to casts formed from impressions of the upperand/or lower jaws of the subject. In additional exemplary aspects, thedisclosed mouth guard can optionally comprise one or more thermosetplastic materials, such as, for example and without limitation, acrylicmaterials. In these aspects, it is contemplated that the thermosetplastic materials can be molded to casts formed from impressions of theupper and lower jaws of the subject. In still other exemplary aspects,it is contemplated that the mouth guard can comprise one or morethermoplastic materials that can be softened in hot water and thenplaced in the mouth of the subject and fit to the upper teeth of thesubject, as is conventionally known in the art. In these aspects, it iscontemplated that the number of dental clinic visits and the amount oflaboratory costs can be significantly reduced. It is furthercontemplated that the accelerometers 30 and processing circuitry 50described herein can be configured to withstand temperatures far abovethe boiling point of water and can easily survive such a fitting.

Optionally, in one aspect, the plurality of accelerometers 30 can beelectrically coupled to a plurality of printed circuit board (PCB)assemblies. For example, in one exemplary aspect, and as shown in FIG.22, the plurality of PCB assemblies can comprise three PCB assembliesspaced about the mouth guard 10 as disclosed herein with respect to theaccelerometers 30. In this aspect, it is contemplated that when theplurality of accelerometers 30 comprises six accelerometers, each PCBassembly can be configured for electrical coupling to twoaccelerometers. Similarly, it is contemplated that when the plurality ofaccelerometers 30 comprises nine accelerometers, each PCB assembly canbe configured for electrical coupling to three accelerometers. Inexemplary aspects, it is contemplated that at least one PCB assembly canbe securely received within a respective receptacle as further describedherein.

Formation of the Mouth Guard

In exemplary aspects, the mouth guard 10 can be formed from impressionsof the teeth and gums of the upper and lower jaws of the subject. Inthese aspects, the impressions can be used to form a cast of thesubject's teeth and gums using conventional methods. The casts of theteeth and gums of the subject can then be scanned using athree-dimensional (3-D) scanner. Alternatively, in other exemplaryaspects, an intraoral 3-D dental scan of at least the teeth, gums, andsoft and hard palate of the upper and lower jaws of the subject can beperformed. It is contemplated that the solid models formed from thescans can be printed in 3-D to form a cast comprising a plasticmaterial, such as, for example and without limitation, AcrylonitrileButadiene Styrene (ABS). It is further contemplated that the 3-D scansof the casts can then be uploaded to a 3-D solid modeling softwarepackage. As shown in FIGS. 19A and 19B, a bridge element 32 can befitted to the scans. It is contemplated that the bridge element 32 canbe configured to fit to the upper jaw such that there is about 2 mm ofclearance between the bridge and the teeth and gums of the subject. Itis further contemplated that a 2 mm thick acrylic thermoplastic sheetcan be vacuum-formed to the cast of the teeth and gums of the upper jawof the subject and trimmed to form the mouth guard. Clearance can beconfirmed between the bridge 32 and the lower jaw, and the bridge 32 canbe adjusted as necessary. As depicted in FIG. 21, it is contemplatedthat the bridge 32 can be constructed of ABS or other plastic materialusing a 3-D printer as is known in the art. It is further contemplatedthat the bridge 32 can be affixed to the mouth guard 10 usingmedical-grade adhesive. In exemplary aspects, it is contemplated that asecond soft layer of thermoplastic material can be heated andvacuum-formed over and bonded to the mouth guard 10, the bridge element32, and at least a portion of the processing circuitry 50. In theseaspects, it is contemplated that the second layer of thermoplasticmaterial can substantially encapsulate and seal at least a portion ofthe processing circuitry 50 and thereby protect the processingcircuitry. It is further contemplated that the second layer ofthermoplastic material can be shaped to make the mouth guard 10 moreergonomic.

In another exemplary aspect, and as shown in FIG. 20, the bridge element32 can be coupled to three receptacles 34 configured to receive aprinted circuit board (PCB) assembly as described herein. In thisaspect, the three receptacles 34 can be spaced about the mouth guard 10and positioned at respective positions, such as, for example and withoutlimitation, the three distinct locations disclosed herein. For example,a first receptacle can be positioned just outside the right molars ofthe subject, a second receptacle can be positioned just outside the leftmolars of the subject, and the third receptacle can be positioned justin front of the central incisors of the subject. In exemplary aspects,as shown in FIG. 22, each receptacle 34 can be configured to receive arespective PCB assembly. In these aspects, each PCB assembly can beaffixed to the receptacles by medical-grade adhesive or anotherconventional adhesive, provided the adhesive is safe for usage withinthe mouth of a subject. It is further contemplated that the PCBassemblies, after being positioned within a respective receptacle, canbe wired and sealed. An exemplary configuration of the PCB assemblies,the accelerometers, the bridge, and wiring of the mouth guard isdepicted in FIG. 23. In exemplary aspects, it is contemplated that thebridge element 32 can define the three receptacles 34. In these aspects,it is contemplated that the three receptacles 34 can be integrallyformed with the bridge element 32.

In operation, it is contemplated that the bridge element 32 can ensurethat the accelerometers 30 are properly positioned. For example, it iscontemplated that the bridge element 32 can be configured to ensure thatthe bottom edges of each receptacle 34 are positioned substantiallywithin a common plane, such as, for example and without limitation, anxy plane. It is further contemplated that the receptacles 34 of thebridge element 32 can be spaced such that the left and right receptaclesare substantially symmetrically positioned relative to the sagittalplane of the subject (containing the central axis 26 of the U-shapedelement 12). It is still further contemplated that the center receptaclecan be positioned such that it is substantially bisected by the sagittalplane of the subject (and the central axis 26 of the U-shaped element12).

Optionally, in some exemplary aspects, it is contemplated that at leasta portion of the mouth guard 10 can be printed with a 3-D printer. Inthese aspects, it is optionally contemplated that substantially theentire mouth guard can be printed with a 3-D printer. It is contemplatedthat the mouth guard can be printed as a single, integral piece or asmultiple pieces to be assembled at a later time. It is furthercontemplated that the mouth guard can optionally comprise a singlematerial. Alternatively, however, it is contemplated that the mouthguard can optionally comprise a plurality of materials. In exemplaryaspects, it is contemplated that the receptacles for the PCB assembliesand other circuitry of the mouth guard can be printed with the 3-Dprinter. In some exemplary aspects, it is contemplated that at least aportion of the mouth guard can be printed with a 3-D printer and atleast a portion of the mouth guard can be manufactured using a differentmanufacturing process, such as those further described herein. Moregenerally, it is contemplated that at least a first portion of the mouthguard can be printed with a first manufacturing process as describedherein and that at least a second portion of the mouth guard can beprinted with a second manufacturing process as described herein.

Alternatively, it is contemplated that some combination of themanufacturing processes described above can be used to create the mouthguard.

As shown in FIG. 24, the linear and angular positions of the mouth guard10 relative to the head of the subject can be identified using biometricmarkers. The center of mass of the head of the subject is positionedjust beneath the zygomatic arch, just in front of the ear. The center ofmass of the head of the subject can generally be found by running one'sfingers along the crest of the cheekbone ridge that runs roughly fromthe eye socket (corresponding to the smiley face marker closest to theeye) back to the ear (corresponding to the smiley face marker closest tothe ear). The left and right crest of the cheekbone ridge generallycorresponds to the transverse plane of the head. The transverse planeintersects the sagittal plane, and a third plane, the coronal plane ofthe head, is orthogonal to those two planes. All three planes intersectat the center of mass of the head. The intersections of the planes formthe fore-aft, left-right, and up-down directions of the head. The rightPCB of the mouth guard can be positioned just inside the cheek and isfound by palpating the cheek (corresponding to the lowest smiley facemarker). It is contemplated that the front PCB can be visible if thesubject's lips are parted. It is contemplated that other biometricmarkers may be identified as important for determining the severity ofhead impact.

Similar positional information for the head of the subject can bedetermined for the opposite (left) side of the head of the subject, andthe positional values are then averaged to give the final positionalinformation for the head of the subject. Using these average values, thelinear and angular positions of the mouth guard relative to the head ofthe subject can be determined.

In use, and with reference to FIGS. 2 and 22-23, it is contemplated thatthe left PCB assembly (and associated accelerometers) can be configuredto measure acceleration in the up-down and fore-aft directions, theright PCB assembly (and associated accelerometers) can be configured tomeasure acceleration in the up-down and fore-aft directions, and thecentral PCB assembly (and associated accelerometers) can be configuredto measure acceleration in the left-right and up-down directions. Theforward direction corresponds with the x direction, the leftwarddirection corresponds with the y-direction, and the upward directioncorresponds with the z direction.

The Processing Circuitry

In a further aspect, and with reference to FIG. 1A, the plurality ofaccelerometers 30 of the mouth guard can be configured for operativecommunication with processing circuitry 50. In this aspect, theprocessing circuitry 50 can be configured to receive the outputs fromthe plurality of accelerometers 30 of the mouth guard 10. In exemplaryaspects, the processing circuitry 50 can function as an integratedcircuit. In other exemplary aspects, the plurality of accelerometers 30and at least portions of the processing circuitry 50 can be embedded inor otherwise secured to the mouth guard.

In still a further aspect, the plurality of accelerometers 30 of themouth guard 10 can be in operative communication with at least one powersource 52. In this aspect, the at least one power source 52 can be inoperative communication with the processing circuitry 50 such that theat least one power source is configured to power the accelerometers 30of the mouth guard 10 and the processing circuitry. It is contemplatedthat the at least one power source 52 can be a conventional battery,capacitor, or electromagnetic power source. Optionally, it is furthercontemplated that the at least one power source 52 can be rechargeablethrough a first port defined in the mouth guard. It is still furthercontemplated that the at least one power source 52 can be removable andreplaceable. In an exemplary aspect, it is contemplated that the atleast one power source 52 can be an electric generator that is poweredby mechanical energy received from the subject. In this aspect, it iscontemplated that the electric generator can be configured to convertmechanical energy applied to the mouth guard by the subject (through,for example, biting down) into electrical energy. It is contemplatedthat the electric generator can optionally be a piezoelectric generatorcomprising one or more materials that exhibit the piezoelectric effect,such as, for example and without limitation, quartz. When coupled withappropriate circuitry, it is contemplated that such piezoelectricgenerators can be configured to generate electrical energy from cyclicmechanical strain.

In one aspect, the processing circuitry 50 can comprise at least onememory 64 in operative communication with the plurality ofaccelerometers 30 of the mouth guard 10. In this aspect, it iscontemplated that the at least one memory 64 can be configured toreceive and store the outputs of the plurality of accelerometers 30 ofthe mouth guard 10. In some aspects, the at least one memory 64 can becoupled to the mouth guard 10. However, in other alternative aspects, itis contemplated that the at least one memory 64 can be positioned at aremote location from the subject.

In another aspect, the processing circuitry 50 can comprise at least onetransmitter 56 in operative communication with at least one of the atleast one memory 64 and the plurality of accelerometers 30 of the mouthguard. In this aspect, it is contemplated that the at least onetransmitter can be configured to transmit one or more outputs stored onthe at least one memory. Optionally, it is contemplated that the atleast one transmitter 56 can be a wireless transmitter configured towirelessly transmit one or more outputs stored on the at least onememory. Alternatively, or additionally, it is contemplated that the atleast one wireless transmitter can be configured to receive and thenwirelessly transmit the outputs from the plurality of accelerometers ofthe mouth guard. Although a wireless transmitter is preferred, it iscontemplated that the at least one memory and the plurality ofaccelerometers can be connected to one another by a conventionalhard-wired connection.

In an additional aspect, it is contemplated that the processingcircuitry 50 can comprise an analog-to-digital converter 54 as isconventionally known in the art. In this aspect, it is contemplated thatthe analog-to-digital converter 54 can be operatively coupled to andpositioned between the plurality of accelerometers 30 and at least oneof a memory 64 and a wireless transmitter 56. It is further contemplatedthat the analog-to-digital converter 54 can be configured to receive theoutputs of the plurality of accelerometers 30 and convert the outputsinto a digital signal configured for further processing by theprocessing circuitry.

In some optional aspects, the processing circuitry 50 can comprise amicrocontroller/data logger 58 in operative communication with one ormore components of the processing circuitry 50. In these aspects, it iscontemplated that the microcontroller 58 can comprise hardware andsoftware that are configured to control the operation of the componentsof the processing circuitry 50 in operative communication with themicrocontroller. For example, it is contemplated that themicrocontroller 58 can be configured to initiate transmission of outputsstored on the at least one memory 64.

In exemplary aspects, the processing circuitry 50 can optionallycomprise a repeater 65 positioned on the person of the subject or inclose proximity to the subject. In these aspects, the repeater 65 can beconfigured to receive the outputs of the plurality of accelerometers 30of the mouth guard 10 from the at least one wireless transmitter 56 orthrough a hardwire connection. It is contemplated that the repeater 65can be a relatively high-power repeater. In other exemplary aspects, theprocessing circuitry 50 can optionally comprise a receiver 66 configuredto receive the outputs from the accelerometers 30 of the mouth guard 10that are stored in the at least one memory 64 of the processingcircuitry. In these aspects, it is contemplated that the receiver 66 canbe configured to receive (i.e., download) the outputs that are stored inthe memory 64 of the processing circuitry 50 in response to theoccurrence of a threshold “trigger” event. It is further contemplatedthat the processing circuitry 50 and/or mouth guard 10 can define asecond port configured to permit electrical coupling between thereceiver 66 and the memory 64 of the processing circuitry such that thereceiver can download the stored output values. It is still furthercontemplated that the processing circuitry 50 can operate in arelatively low-power state in which the outputs of the accelerometers 30are not recorded until the occurrence of a threshold event, such as, forexample and without limitation, acceleration at a rate higher than apredetermined threshold value. Upon occurrence of the threshold event,the processing circuitry 50 can shift to an active mode in which theoutputs of the accelerometers 30 are recorded.

Optionally, in various aspects, it is contemplated that the processingcircuitry 50 can comprise a base station that is positioned remotelyfrom the subject. In these aspects, the wireless transmitter of theprocessing circuitry can optionally be configured to transmit theoutputs (following analog-to-digital conversion, as appropriate) of theaccelerometers to the base station. Alternatively, the base station canbe operatively coupled to the repeater, and the outputs received by therepeater can be transmitted to the base station. In exemplary aspects,the base station can comprise a memory. Optionally, it is contemplatedthat the base station can be a computer 67 having a processor 68 and amemory 69 in communication with the processor. In exemplary aspects, thecomputer 67 can comprise a wireless receiver 66 configured to receivethe outputs of the accelerometers.

The Helmet

In further aspects, and with reference to FIG. 1C, a helmet 40 can beprovided for receiving at least a portion of the head of the subject. Inthese aspects, the helmet can have a wall 42 that defines an innerchamber 44. The inner chamber 44 of the helmet 40 can be configured toreceive the head of the subject. In an additional aspect, the helmet 40can comprise a plurality of accelerometers 46 operatively associatedwith the wall 42 of the helmet. In this aspect, the plurality ofaccelerometers 46 can be spaced from one another about the helmet 40. Itis contemplated that each accelerometer 46 of the plurality ofaccelerometers can be configured to produce an output indicative of thelinear and angular acceleration of the helmet.

In exemplary aspects, it is further contemplated that the helmet 40 canbe operatively coupled to a plurality of accelerometers 46 andprocessing circuitry 50 in the manner described above with respect tothe mouth guard 10. In these aspects, the processing circuitry 50 can beconfigured to convert the outputs from the plurality of accelerometers46 into an output indicative of the linear and angular acceleration ofthe head of the subject.

In other exemplary aspects, the helmet 40 and the mouth guard 10 can beused simultaneously in a cooperative system 10 for determining thelinear and angular accelerations of the head of the subject. In theseaspects, it is contemplated that the helmet 40 and the mouth guard 10can comprise the same number of accelerometers 30, 46. It is furthercontemplated that the accelerometers 46 of the helmet 40 can optionallybe oriented and positioned in an orientation and position that generallycorresponds to that of the accelerometers 30 of the mouth guard 10.Thus, in exemplary aspects, it is contemplated that the accelerometers46 of the helmet can optionally be spaced about the helmet 40 within acommon plane, which, optionally, can be parallel to the plane of theaccelerometers 30 of the mouth guard 10. In these aspects, it is furthercontemplated that the accelerometers 46 can optionally be provided asclusters of at least one accelerometer, with each cluster ofaccelerometers positioned at a distinct location about the helmet. It isfurther contemplated that the accelerometers 46 can optionally beprovided in three clusters of at least one accelerometer, with eachcluster being positioned at a distinct location. Optionally, thedistinct locations can comprise a first location proximate the rightside of the head of the subject, a second location proximate the leftside of the head of the subject, and a third location proximate a centerportion of the head of the subject, such as, for example and withoutlimitation, a location proximate the forehead of the subject or alocation proximate the back or rear portion of the head of the subject.In further exemplary aspects, it is contemplated that at least portionsof the processing circuitry 50 can be in operative communication withthe accelerometers 30, 46 of both the mouth guard 10 and the helmet 40.Alternatively, the mouth guard 10 and the helmet 40 can be in operativecommunication with distinct sets of processing circuitry as describedherein.

Exemplary Methods

In use, the helmet and/or mouth guard, in conjunction with theprocessing circuitry, can be used in a method for determining the linearand angular acceleration of the head of the subject. In one aspect, thehead of the subject can be positioned within the inner chamber of thehelmet. In another aspect, the mouth guard can be positioned inengagement with at least one of the upper teeth and the lower teeth ofthe subject. In an additional aspect, the method can comprise deliveringa first impact force to the helmet. In response to delivery of the firstimpact force, each accelerometer of the plurality of accelerometers ofthe helmet can be configured to produce an output indicative of thelinear and angular acceleration of the helmet. Similarly, eachaccelerometer of the plurality of accelerometers of the mouth guard canbe configured to produce an output indicative of the linear and angularacceleration of the mouth guard. Thus, the accelerometers of the helmetand the mouth guard can simultaneously record impact and accelerationdata. It is contemplated that the accelerations measured by theaccelerometers 30 of the mouth guard 10 substantially correspond to theaccelerations actually experienced by the head of the subject.

In a further aspect, the method can comprise transmitting the outputs ofthe accelerometers of the helmet and the mouth guard to the processingcircuitry. In another aspect, the method can comprise determining,through the processing circuitry, a transfer function configured toconvert the outputs of the accelerometers of the helmet to the outputsof the accelerometers of the mouth guard. In this aspect, it iscontemplated that this step can be repeated for a series of impactforces that are applied to the helmet in order to improve the accuracyof the transfer function.

In an additional aspect, the method can comprise disengaging the mouthguard from the teeth of the subject and, subsequently, removing themouth guard from the mouth of the subject. In this aspect, it iscontemplated that, after the transfer function is known, theacceleration and impact experienced by the head of the subject can bedetermined based solely on the acceleration and impact data recorded bythe accelerometers of the helmet; thus, the subject does not have tocontinue wearing the mouth guard. In still another aspect, the methodcan comprise delivering a second impact force to the helmet. In responseto delivery of the second impact force, each accelerometer of theplurality of accelerometers of the helmet can be configured to producean output indicative of the linear and angular acceleration of thehelmet.

In still another aspect, the method can comprise transmitting theoutputs of the accelerometers of the helmet to the processing circuitry.In a further aspect, the method can comprise applying, through theprocessing circuitry, the transfer function to the outputs of theaccelerometers of the helmet to determine the acceleration of the headof the subject.

In another exemplary method, it is contemplated that a database of headacceleration event characteristics, head injuries, treatments, andresults can be developed into a tool for providing information to asubject regarding diagnosis, suggested treatment, and prognosis. Theacceleration event characteristics within the database can include peaklinear and angular accelerations recorded for the subject, the durationof an acceleration above a predetermined threshold, and othercharacteristics that provide information regarding the amount and typesof accelerations experienced by the head of the subject. In one aspect,in operation, the method can comprise downloading head accelerationoutputs from the plurality of accelerometers of a mouth guard and/or ahelmet as described herein. In this aspect, the method can furthercomprise, through a processor in communication with the database,determining possible head injuries and/or symptoms associated with theacceleration outputs. In another aspect, the method can compriseproviding an input to the database indicative of symptoms exhibited by asubject. In this aspect, the method can further comprise, through aprocessor in communication with the database, determining possibletreatments and associated prognoses for the symptoms exhibited by thesubject. Typically, in operation, it is contemplated that a medicaltechnician can download the acceleration outputs from the mouth guardand/or the helmet, the acceleration data can be evaluated using thedatabase, and treatment of the subject can be initiated in the traumacenter or even during transport of the subject to the trauma center. Inexemplary sports applications, it is contemplated that, after an impactduring a game, the acceleration data from the mouth guard and/or helmetcan be downloaded and evaluated to determine if an athlete should beallowed to return to play. It is contemplated that the downloadedacceleration information can be particularly useful when the subject isunconscious or otherwise unable to report symptoms or aid in diagnosis.It is still further contemplated that conscious athletes or soldiers areoften eager to return to play or duty and are uncooperative ordismissive of suggestions of the severity of the traumatic injury theyhave experienced. Thus, it is contemplated that the use of thedownloaded acceleration data can help inform physicians, coaches, andofficials of the severity of the head injury experienced by the subject.

In further exemplary aspects, it is contemplated that the disclosedmouth guard and/or helmet can be worn by all athletes participating inregulated play and all soldiers participating in training or combat. Forexample, in boxing, where a knockout determines the outcome of a fight,it is contemplated that the disclosed devices, systems, and methods canbe used to verify the legitimacy of a knockout based upon the recordedacceleration data. In another exemplary application, the discloseddevices, systems, and methods can be used during rehabilitation ofsoldiers, stroke victims, and other patients with compromised balance toensure that any head traumas of the patient are recorded. It is furthercontemplated that, because specific motions of the head can be relatedto compromised balance, head injury, and falls, the disclosed devices,systems, and methods can be used in diagnostics, therapy, and monitoringof individuals with verified or suspected compromised balance or headinjury. In still further exemplary applications, it is contemplated thatparents can require their children to wear the disclosed devices duringactivities associated with a significant risk of head impact, such as,for example, skateboarding and bicycle riding.

The Algorithm for Analyzing Acceleration Data from the Mouth Guardand/or Helmet

An exemplary algorithm for analyzing acceleration data from the mouthguard is described below. Although the algorithm is described withrespect to a mouth guard configuration in which three three-axisaccelerometers were used, it is contemplated that a similar overallmethod can be adapted to any accelerometer configuration describedherein.

Each 3-axis accelerometer of the mouth guard can have a local orthogonal3-axis accelerometer coordinate system that is configured to measure thelinear accelerations in the directions of those coordinate axes. Thealgorithm for analyzing the acceleration data is determined by thefollowing procedure: 1) Establishing an orthogonal local mouth guardcoordinate system (for example, oriented in the forward, left side, andupward directions with the forward and left side directions in the planeof the bite of the molars and the upward direction perpendicular to thatplane); 2) Determining the position and orientation of each local 3-axisaccelerometer coordinate system in the local mouth guard coordinatesystem; 3) Transforming the 3-axis accelerometer measured linearaccelerations to the local mouth guard coordinate system; 4) Determiningthe angular accelerations of the mouth guard in the local mouth guardcoordinate system from the linear accelerations in the local mouth guardcoordinate system; 5) Determining the linear accelerations of the originof the local mouth guard coordinate system in the local mouth guardcoordinate system; 6) Determining the position of the head center ofmass and establishing an orthogonal local head coordinate system withits origin at the head center of mass (for example, oriented in theforward, left side, and upward directions); 7) Determining the positionand orientation of the local mouth guard coordinate system in the localhead center of mass coordinate systems; 8) Transforming the angularaccelerations in the local mouth guard coordinate system to the angularaccelerations in the local head center of mass coordinate system; and 9)Determining the linear accelerations of the head center of mass in thelocal head center of mass coordinate system from the mouth guard linearand angular accelerations in the local mouth guard coordinate system. Inexemplary aspects, it is contemplated that steps 3) through 9) can bemathematically combined into a single step. It is contemplated that theacceleration of points other than the center of mass may be identifiedas important for determining the severity of head impact and can bedetermined using similar methods.

As shown in FIG. 1A, the mouth guard can optionally comprise powersupplies, accelerometers, analog-to-digital converters, transmitters,data loggers, amplifiers, and/or antennas as are known in the art.However, it is contemplated that the way in which the acceleration datais stored and recovered can significantly impact the complexity, sizeand power requirements of the device. For example, it is contemplatedthat storing the data for downloading using a hardwire connection at alater time can significantly reduce the complexity, size and powerrequirements of the mouth guard electronics.

It is contemplated that the minimum number of accelerometers required todetermine the angular and linear accelerations of the head center ofmass (or other point) is six. It is further contemplated that if onlylinear accelerometers are used, those six linear accelerometers are mostconveniently configured as three 2-axis accelerometer packages that aresubstantially aligned with the local orthogonal mouth guard coordinatesystem axes as shown in FIG. 2. It is still further contemplated thatthis configuration can significantly decrease the complexity of thedevice by reducing the number of accelerometers from nine to six,significantly decrease the amount of data collected from theaccelerometers by reducing the number of channels from nine to six,significantly decrease the complexity and amount of the data analysis,and significantly increase the accuracy of the linear and angularaccelerations of the head center of mass (or other point) results. It iscontemplated that the data analysis algorithm for the three 2-axisaccelerometer configuration can be substantially the same as the three3-axis accelerometer configuration except that steps 1-3 can besimplified.

As shown in FIG. 2, six linear accelerometers, two on the right side ofthe mouth guard, two center accelerometers, and two left accelerometers,can be used to measure the linear accelerations a_(Rx), a_(Rz), a_(Cy),a_(Cz), a_(Lx), and a_(Lz). The xyz axes are orthogonal. Theaccelerometers lie on the xy plane and are positioned symmetricallyrelative to the xz plane. The accelerometer measurement axes areparallel to the xyz axes. The length of the mouth guard measured fromthe midpoint between the two left accelerometers and two rightaccelerometers to the two center accelerometers is d_(x), and the widthof the mouth guard measured from the two left accelerometers to the tworight accelerometers is d_(y). Rigid body kinematic analysis can be usedto determine the angular and linear accelerations of the mouth guard atthe origin O from the measured linear accelerations. In the mouth guardcoordinate system xyz, if the linear acceleration terms due to theangular velocities are ignored, the angular accelerations α_(x), α_(y),and α_(z) can be determined from the linear accelerations a_(Rx),a_(Rz), a_(Cy), a_(Cz), a_(Lx), and a_(Lz) using the followingequations:

${\alpha_{x} = {\left( {a_{Lz} - a_{Rz}} \right)/d_{y}}},{\alpha_{y} = {\left( {\frac{a_{Rz} + a_{Lz}}{2} - a_{Cz}} \right)/d_{x}}},$and α_(z)=(a_(Rx)−a_(Lx))/d_(y). In the mouth guard coordinate systemxyz, if the linear acceleration terms due to the angular velocities areignored, the linear accelerations of point O, a_(Ox), a_(Oy), anda_(Oz), can be determined using the following equations:a_(Ox)=(α_(Lx)+a_(Rx))/2,a_(Oy)=a_(Cy)−α_(z)d_(x)=a_(Cy)−(a_(Rx)−a_(Lx))d_(x)/d_(y), anda_(Oz)=(a_(Lz)+a_(Rz))/2. It is contemplated that these accelerations ofthe mouth guard can be used to determine the acceleration of any pointon the skull, including the head center of mass.

FIG. 3 shows the head coordinate system axes u, v, and w and origin andcenter of mass G relative to the local mouth guard coordinate systemaxes x, y, and z and origin O. The uvw axes are orthogonal. The y and vaxes are parallel, and the xz and uw planes and origins O and G are onthe sagittal plane. The u axis points forward, the v axis pointsleftward, and the w axis points upward. The approximate location of thehead center of mass is found by following the left and right zygomaticridge back to just in front of the ear—the head center of mass islocated between those two points on the sagittal plane, and those twopoints lie on the v axis. The plane formed by the left and rightzygomatic arches and the sagital plane intersect along the u axis. Thexyz coordinate system is rotated an angle β relative to the uvwcoordinate system. The xyz origin O is a distance h_(u) in the forwardor u direction and a distance h_(w) in the downward or negative wdirection from the uvw origin G. The head center of mass coordinatesystem origin G and axes uvw are used as the reference coordinate systemorigin and axes to compare head accelerations from one individual to thenext. If the head and mouth guard system is treated as a rigid body,then the angular accelerations of the head center of mass, α_(u), α_(v),and α_(w), are as follows: α_(u)=α_(x) cos(β)+α_(z) sin(β), α_(v)=α_(y),and α_(w)=−α_(x) sin(β)+α_(z) cos(β). If the linear acceleration termsdue to the angular velocities are ignored, the linear accelerations ofthe head center of mass, a_(Gu), a_(Gv), a_(Gw), are as follows:a_(Gu)=a_(Ox) cos(β)+a_(Oz) sin(β)+h_(v)α_(v),a_(Gv)=a_(Oy)−h_(v)α_(u)−h_(u)α_(w), and a_(Gw)=−a_(Ox) sin(γ)+a_(Oz)cos(β)+h_(u)α_(v). The accelerations of the head center of mass, α_(u),α_(v), α_(w), a_(Gu), a_(Gv), and a_(Gw), can be used to determine theseverity of a head impact.

The following examples are offered by way of illustration and not by wayof limitation

Experimental Example One

The accelerations of the head during soccer ball heading were recordedby introducing a mouth guard instrumented with a dual-axis linearaccelerometer chip. The accelerometer chip was hardwired to a dataacquisition unit and powered by a chemical battery.

Increasing concern about health and safety in youth sports has broughtattention to the possible cumulative head trauma of soccer ball heading.Studies into a possible correlation between soccer heading and cognitivedysfunction, the effectiveness of soccer headgear, and the accelerationof the head during the heading maneuver are well-documented. Paris etal., “Soccer Ball Heading Model,” Proceedings of the ASME 2008 SummerBioengineering Conference (SBC2008) June 25-29, Marriott Resort, MarcoIsland, Fla., USA (2008), which is incorporated by reference herein inits entirety, proposed an impulse momentum formulation to model theimpact between the soccer ball and the head. To verify the theory, asoccer ball was dropped on a solid resin sphere of equal radius andfixture on a force plate. The numerical results of the model agreed wellwith the experimental results for impact force, impact duration, andimpulse vs. impact velocity. The analytical model effectivelyrepresented the impact of a soccer ball on a rigid spherical surface ofequal diameter.

The test subject was an 18-year-old male in good physical condition, 168cm tall and with a mass of 70 kg. The subject was asked perform a properheading maneuver on a ball that would be launched toward his head. Asoccer player performing a heading motion usually jumps and moves thehead anteriorly in an offensive movement, causing a much greater impulseon the head than if he or she stood still. Such a motion includesadducting the neck in the sagittal plane simultaneously with the impactof the ball (FIG. 4).

A Baden 150 soccer ball, inflated to 55 kPa, was used. A JUGS® SoccerMachine was used to deliver the ball at four different launch speeds.The subject was fitted with a custom acrylic mouth guard that encased anAD ADXL250 Dual Axis Accelerometer Chip with the X-axis orientedanteriorly and the Y-axis superiorly (FIGS. 5A and 5B). Theaccelerometer was wired to a DATAQ data acquisition unit and an HPlaptop with DATAQ data acquisition software. All experimental trialswere performed indoors to eliminate the effects of wind.

The subject stood at four different distances from the launcher to carryout the heading maneuver at four different launch speeds. Approximateimpact velocities were calculated based on the initial velocity andprojectile kinematics. The DATAQ software sampled at 10 kHz. The outputvoltage amplitude was directly proportional to the magnitude of theacceleration of the chip. One g (9.81 m/s/s) corresponded to 0.38 mVoutput.

Each set of impact data was isolated and smoothed using a five-pointmoving average since the period of the noise was usually three to foursamples long. From this smoothed data, the peak positive and negativeaccelerations were averaged and plotted against velocity.

FIG. 6 shows unfiltered data from a 9.6 m/s impact. FIG. 7 shows thesame data filtered by a five-point moving average. Here, the peaks aremore defined and are not just spikes from noise. All the peakaccelerations for each velocity were averaged and graphed againstvelocity with best fit linear trend lines in FIG. 8.

The results demonstrated the use of an accelerometer-chip instrumentedmouth guard. A maximum 34 g's of head acceleration was observed from amere 11.2 m/s ball launch. It has been suggested that most headingmaneuvers are performed on balls traveling at up to 18.1 m/s, whichwould cause even greater head accelerations. Even though the duration ofsuch accelerations is on the order of only a few milliseconds, there isconcern that the repetitive nature of heading may cause neuro-cognitivedamage.

The data demonstrated a high correlation between maximum headacceleration and impact velocity. The data also showed a relationshipconsistent with that presented in the numerical impulse-momentum modeland experimental results discussed by Paris et al. (2008)

Experimental Example Two

The following experimental example is further described in Kara et al.,“Evaluation of an Instrumented Mouthguard to Measure the Accelerationsof the Head due to Soccer Ball Heading,” Proceedings of PACAM XII, 12thPan-American Congress of Applied Mechanics (Jan. 2-6, 2012, Port ofSpain, Trinidad), which is incorporated by reference herein in itsentirety.

An exemplary mouth guard with nine spatially separated accelerometersconfigured as three spatially-separated three-axis accelerometers and amicrocontroller with a data logger and a wireless transmitter was builtand tested.

Recent concern about the potential cumulative effects of head impacts,even those not severe enough to cause loss of consciousness, in youth,college, amateur and professional athletes has led to increased researchin this area. Soccer is a unique sport in that the unprotected head isdeliberately used to direct the motion of the ball during play. Headinjuries account for approximately 4-15% of all injuries experienced bysoccer players, depending on the population surveyed. While the possiblelong-term effects of heading are still subject to debate, there isevidence which suggests that it is responsible for transientneurocognitive deficits and transient concussion symptoms. In order forthe highest-risk sports and individuals to be identified, tools areneeded that can quantitatively measure the levels of head accelerationexperienced by athletes in a variety of situations.

This experimental example tested a wireless, instrumented mouth guardthat was capable of measuring accelerations of the head resulting fromimpact forces, specifically resulting from soccer ball heading. In thework presented here, three 3-axis accelerometers were used, allowingboth linear and angular accelerations of the head to be determined. Itis contemplated that such instrumentation can (1) provide insight intothe still-debated issue of whether heading is potentially dangerous bydirectly examining the biomechanics of heading, and (2) lead to thedevelopment of instrumentation that could potentially provide the meansfor quantitative assessment of any type of head impact injury.

The subject of this research was an 18-year-old female soccer player ingood physical condition, with a height of 175 cm and a mass of 69 kg. Acustom acrylic mouth guard, pictured in FIG. 9, was created from a moldof the subject's teeth and instrumented with three 3-axismicroelectromechanical system (MEMS) accelerometers (Analog Devices,ADIS 16223). These accelerometers, labeled (R), (C) and (L) in FIG. 9,were capable of measuring large accelerations with high acquisitionrates (±70 g, 14 kHz), and were small enough in mass to avoidsignificant inertial effects on the player's head. Referring to FIG. 10,the accelerometers were used to determine the linear accelerations ofthe subject's head in the x-, y- and z-directions, and the spatialseparation of the accelerometers allowed the angular accelerations aboutthe x-, y- and z-axes, as well as the linear accelerations of thesubject's head center of mass, to be determined. The mouth guardcontained a wireless transmitter, labeled in FIG. 9, which sent data toa wireless data logger connected to a laptop computer. The wirelessaspect of this device allowed the subject to move normally without beingtethered to a data acquisition system.

During experimentation, a soccer ball launching machine (Sports SoccerMachine M1800, Jugs Sports Equipment) was used to launch balls at thetest subject, who was asked to perform heading maneuvers consistent withthose ordinarily performed during practice and game play. The balls werelaunched at speeds up to approximately 12 m/s. A standard size 5 soccerball, inflated to 62 kPa, was used. Experiments were performed indoorsto eliminate the effects of wind. Each heading event was recorded usinga high speed (HS) camera (HotShot 512 INT, NAC Image Technology) capableof recording up to 2,000 fps at its full resolution of 512×512 pixels.Contact between the ball and head typically lasted tens of milliseconds,allowing between 20 and 30 frames to be captured over the course of theimpact. This allowed the time evolution of the ball geometry, as well asthe ball and head positions and the impact force between the two, to bestudied in much greater detail. Frame-by-frame analysis of each videowas performed using the Image Processing Toolbox available with MATLAB.The position of the ball was determined in each frame, as well as itsgeometric deflection during contact with the head. The pre- andpost-impact velocities, and the impulse delivered by the ball to thehead, were calculated from this information.

An example of the type of data collected for a typical heading event ispresented here. The coordinate system used to describe the accelerationresults is shown in FIG. 10. The center of mass (CG) of the head wasassumed to lie at the sagittal plane, approximately beneath thezygomatic arch. The raw data collected by the mouth guard for eachheading event included linear accelerations in the x-, y- andz-directions for each of the three attached accelerometer sensors in thelocal coordinate system for that sensor. FIG. 11 shows transformedaccelerometer traces for the global x-, y- and z-directions (FIG. 10)from each sensor for one particular heading event. Frame-by-frameanalysis of the HS video captured during this heading event reveals thatthe absolute value of ball velocity was approximately 9.9 m/spre-impact, and approximately 7.4 m/s post-impact. A single frame fromthe HS video captured for this event, showing the maximum geometricdeformation of the ball, is shown in FIG. 12. For the heading eventpictured in FIG. 12, the HS camera captured 26 frames where the ball andhead were in contact, making the duration of the impact equal toapproximately 13 ms. The force F delivered to the head from the ball wasdetermined as a function of time throughout the heading event usingF=pπd²/4, where p is the pressure in the ball and d is the diameter ofthe contact patch between the ball and the player's head measured fromthe HS video. In this case, the ball pressure was 62 kPa. Change inpressure was neglected. The force imparted to the head by the ball isshown in FIG. 13 as a function of time. The total impulse delivered bythe ball was calculated by integrating the force shown in FIG. 12 as afunction of time over the course of the entire impact. This integrationyielded a total impulse of 7.01 N-s for the profile shown in FIG. 12. Asa validation of the impulse, the impulse was compared with the change inmomentum of the ball, and very good agreement was found.

A total of six heading events were recorded using the techniquedescribed above. The headers were performed at a variety of speedsranging up to approximately 12 m/s. The total delivered impulse is shownplotted as a function of initial ball velocity in FIG. 14. The linearaccelerations measured by the left, right and center accelerometers(FIG. 11) were transformed to give the linear accelerations of the headCG in the x-, y- and z-directions, and the angular acceleration of thehead about the x-, y- and z-axes, using rigid-body mechanics. For theheader shown in FIG. 11, the angular accelerations of the head about thex-, y- and z-axes are shown in FIG. 15, and the linear accelerations ofthe head CG in the x-, y- and z-directions are shown in FIG. 16. Thepeak magnitude of the linear acceleration of the head CG in the sagittalplane is shown in FIG. 17 as a function of initial ball velocity. Alinear acceleration of as high as 25 g's was observed for an initialball velocity of 9.9 m/s.

The peak angular accelerations of the head about the y-axis, a_(y), areshown in FIG. 18. An angular acceleration α_(y) having an absolute valueof as high as 3500 rad/s² was observed for an initial ball velocity of11.7 m/s. Angular velocities about the x- and z-axes, α_(x) and α_(z),were generally not appreciable for the headers recorded during thisexperiment, which focused on headers in which the impact between thesoccer ball and the head is frontal and lies along the sagittal plane.It is not unheard of for soccer players to use other parts of the headto direct the motion of the ball. Thus, it is contemplated that anon-frontal header can result in appreciable angular accelerations aboutthe x- and/or z-axes as well.

The data presented here supported a linear relationship betweenpre-impact ball velocity and delivered impulse, maximum linearacceleration of the head, and maximum angular acceleration of the headα_(y). The results demonstrated successful use of a custom mouth guardinstrumented with three 3-axis accelerometers to determine both linear(CG) and angular accelerations of the head during soccer ball heading.It is expected that this instrumentation might be used in othersituations where accelerations of the head are of interest.

Experimental Example Three

The following experimental example is further described in Birmingham etal., “An Instrumented Mouthguard to Measure Head Accelerations due toImpact,” Proceedings of the ASME 2013 Summer Bioengineering Conference(SBC2013), June 26-29, Sunriver, Oreg., USA (2013), which isincorporated herein by reference in its entirety.

It is contemplated that, in the long term, quantitative measurementsindicating the magnitude and nature of head impacts can be essential tounderstanding the biomechanics of head injury. Tools are needed that canquantitatively measure the levels of head acceleration experienced byathletes in a variety of situations in order to assess these risks. Thedisclosed experiment was aimed at developing instrumentation that iscomfortable enough to use in the field and which can repeatably andaccurately measure head accelerations from blows to the head. Soccer isa unique sport in that the unprotected head is deliberately used todirect the motion of the ball during play, which makes it practical tostudy in a controlled laboratory setting. While the possible long-termeffects of heading are still subject to debate, there is evidence whichsuggests that it is responsible for transient neurocognitive deficitsand transient concussion symptoms. The work presented here demonstratesthe use of six 1-axis accelerometers, which make the mouthguard moreslim and comfortable while allowing both linear and angularaccelerations of the head to be determined.

The subject of this research was a 25-year-old male soccer player ingood physical condition, with a height of 183 cm and a mass of 92 kg. Acustom acrylic mouthguard, pictured in FIG. 23, was created from a moldof the subject's teeth and instrumented with six 1-axismicroelectromechanical system (MEMS) accelerometers (Analog Devices,ADXL001), capable of measuring large accelerations with high acquisitionrates (±70 g, 30 kHz), but of small enough mass to avoid significantinertial effects on the player's head.

The mouthguard was connected to a microcontroller, which wirelessly sentdata to a data logger and laptop computer. During experimentation, asoccer ball launching machine (Sports Soccer Machine M1800, Jugs SportsEquipment) was used to launch balls at the test subject at speeds up toapproximately 12 m/s. A standard size 5 soccer ball with diameter 22-23cm, mass 0.43 kg, inflated to 62 kPa, was used. Experiments wereperformed indoors to eliminate wind. Each heading event was recordedusing a high speed (HS) camera (HotShot 512 INT, NAC Image Technology)capable of recording up to 2,000 fps at its full resolution of 512×512pixels. Contact between the ball and head typically lasts tens ofmilliseconds, allowing between 20 and 30 frames to be captured over thecourse of the impact. Frame-by-frame analysis of each video wasperformed using the Image Processing Toolbox available with MATLAB. Theposition of the ball was determined in each frame, as well as itsgeometric deformation during contact with the head. The pre- andpost-impact velocities and the impulse delivered by the ball to the headwere calculated from this information. The position of the head wastracked frame-by-frame just prior to impact, allowing the pre-impacthead velocity to be determined. For lower initial ball velocities, wherehead velocity was appreciable, the relative impact speed between theball and head was estimated by adding the incoming ball velocity withthe pre-impact head velocity.

A total of forty-nine heading events were recorded using the techniquedescribed above, at incoming ball speeds between approximately 4 and 12m/s. The peak force of the ball on the head as a function of relativeimpact velocity is shown in FIG. 25.

The linear accelerations measured by the left, right and centeraccelerometers were transformed to give the linear accelerations of thehead CG in the x-, y- and z-directions, and the angular acceleration ofthe head about the x-, y- and z-axes, using rigid-body mechanics. Thecenter of mass (CG) of the head is assumed to lie at the saggital plane,approximately beneath the zygomatic arch. The peak magnitude of thelinear acceleration of the head CG in the saggital (xz) plane is shownin FIG. 26 as a function of relative ball velocity. The coordinatesystem used to describe the acceleration results is shown in the insetin FIG. 27. Linear acceleration ranged as high as 19 g's for a relativeball velocity of 11.6 m/s. The peak magnitude of the angularacceleration of the head about the y-axis, a_(y), is shown in FIG. 27.The absolute value of angular acceleration α_(y) ranged as high as 1852rad/s² for a relative ball velocity of 10.9 m/s. Angular velocitiesabout the x- and z-axes, α_(x) and α_(z), were generally not appreciablefor the headers recorded during this experiment, which has focused onfrontal headers.

The data presented here suggest a linear relationship between pre-impactvelocity and delivered force, maximum linear acceleration of the head,and maximum angular acceleration of the head α_(y). The resultspresented here demonstrate successful use of a custom mouthguardinstrumented with six 1-axis accelerometers to determine both linear(CG) and angular accelerations of the head during soccer ball heading.

Exemplary Aspects

In one exemplary aspect, a mouth guard for determining the linear andangular acceleration of the head of a subject is provided. The subjectcan have a head and upper and lower teeth. The mouth guard can comprisea U-shaped element having an outer side wall, an inner side wall, and atleast one biting surface, the outer side wall, the inner side wall, andthe at least one biting surface cooperating to define at least onechannel configured to receive the upper teeth of the subject. The mouthguard can further comprise a plurality of accelerometers operativelyassociated with the U-shaped element, the plurality of accelerometersbeing spaced from one another about the U-shaped element, eachaccelerometer of the plurality of accelerometers being configured toproduce an output indicative of the linear and angular acceleration ofthe mouth guard.

In another exemplary aspect, the plurality of accelerometers comprise atleast one accelerometer positioned at a first location about theU-shaped element, at least one accelerometer positioned at a secondlocation about the U-shaped element, and at least one accelerometerpositioned at a third location about the U-shaped element, wherein thefirst, second, and third locations are spaced from one another about anarc defined by the U-shaped element.

In another exemplary aspect, the plurality of accelerometers comprise afirst cluster of at least two accelerometers positioned at the firstlocation, a second cluster of at least two accelerometers positioned atthe second location, and a third cluster of at least two accelerometerspositioned at the third location, and each accelerometer of theplurality of accelerometers is configured to measure linear accelerationin a single axis.

In another exemplary aspect, at least one accelerometer of the first,second, and third clusters is configured to measure linear accelerationin a first axis, at least one accelerometer of the first, second, andthird clusters is configured to measure linear acceleration in a secondaxis, and the first axis is perpendicular to the second axis.

In another exemplary aspect, the plurality of accelerometers aresubstantially co-planar.

In another exemplary aspect, the mouth guard comprises first, second,and third receptacles coupled to the outer side wall of the mouth guard,the first receptacle is configured to receive the first cluster ofaccelerometers, the second receptacle is configured to receive thesecond cluster of accelerometers, and the third receptacle is configuredto receive the third cluster of accelerometers.

In another exemplary aspect, the plurality of accelerometers comprise afirst cluster of at least three accelerometers positioned at the firstlocation, a second cluster of at least three accelerometers positionedat the second location, and a third cluster of at least threeaccelerometers positioned at the third location, and each accelerometerof the plurality of accelerometers is configured to measure linearacceleration in a single axis.

In another exemplary aspect, at least one accelerometer of the first,second, and third clusters is configured to measure linear accelerationin a first axis, at least one accelerometer of the first, second, andthird clusters is configured to measure linear acceleration in a secondaxis, at least one accelerometer of the first, second, and thirdclusters is configured to measure linear acceleration in a third axis,and the first axis, the second axis, and the third axis areperpendicular to one another.

In another exemplary aspect, each accelerometer of the plurality ofaccelerometers is configured to measure linear acceleration intwo-perpendicular axes.

In another exemplary aspect, each accelerometer of the plurality ofaccelerometers is configured to measure linear acceleration in threeperpendicular axes.

In another exemplary aspect, the U-shaped element defines opposed firstand second ends, the U-shaped element is substantially symmetrical abouta central axis, the first location is proximate the first end of theU-shaped element, the second location is proximate the second end of theU-shaped element, and the central axis intersects the third location.

In one exemplary aspect, a system for determining the linear and angularacceleration of the head of a subject is provided. The system cancomprise a mouth guard as disclosed herein and processing circuitry inoperative communication with the plurality of accelerometers of themouth guard. The processing circuitry can be configured to receive theoutputs from the plurality of accelerometers.

In an additional exemplary aspect, a method of determining the linearand angular acceleration of the head of a subject is provided. Themethod can comprise positioning the head of the subject within a helmet,the helmet having a wall defining an inner chamber configured to receivethe head of the subject, the helmet comprising a plurality ofaccelerometers operatively associated with the wall of helmet, theplurality of accelerometers being spaced from one another about thehelmet. The method can further comprise positioning a mouth guard inengagement with the upper teeth of the subject, the mouth guardcomprising a U-shaped element and a plurality of accelerometersoperatively associated with the U-shaped element, the plurality ofaccelerometers being spaced from one another about the U-shaped element.The method can further comprise delivering a first impact force to thehelmet, wherein, in response to delivery of the first impact force, eachaccelerometer of the plurality of accelerometers of the helmet isconfigured to produce an output indicative of the linear and angularacceleration of the helmet and each accelerometer of the plurality ofaccelerometers of the mouth guard is configured to produce an outputindicative of the linear and angular acceleration of the mouth guard.The method can further comprise transmitting the outputs of theaccelerometers of the helmet and the mouth guard to processingcircuitry. The method can further comprise determining, through theprocessing circuitry, a transfer function configured to convert theoutputs of the accelerometers of the helmet to the outputs of theaccelerometers of the mouth guard. The method can further comprisedisengaging the mouth guard from the teeth of the subject. The methodcan further comprise delivering a second impact force to the helmet,wherein, in response to delivery of the second impact force, eachaccelerometer of the plurality of accelerometers of the helmet isconfigured to produce an output indicative of the linear and angularacceleration of the helmet. The method can further comprise transmittingthe outputs of the accelerometers of the helmet to the processingcircuitry. The method can still further comprise applying, through theprocessing circuitry, the transfer function to the outputs of theaccelerometers of the helmet to determine the linear and angularacceleration of the head of the subject.

Although several embodiments of the invention have been disclosed in theforegoing specification, it is understood by those skilled in the artthat many modifications and other embodiments of the invention will cometo mind to which the invention pertains, having the benefit of theteaching presented in the foregoing description and associated drawings.It is thus understood that the invention is not limited to the specificembodiments disclosed hereinabove, and that many modifications and otherembodiments are intended to be included within the scope of the appendedclaims. Moreover, although specific terms are employed herein, as wellas in the claims which follow, they are used only in a generic anddescriptive sense, and not for the purposes of limiting the describedinvention, nor the claims which follow.

What is claimed is:
 1. A method of determining linear and angularacceleration of the head of a subject, the subject having a head andupper and lower teeth, the method comprising: positioning the head ofthe subject within a helmet, the helmet having a wall defining an innerchamber configured to receive the head of the subject, the helmetcomprising a plurality of accelerometers operatively associated with thewall of helmet, the plurality of accelerometers being spaced from oneanother about the helmet; positioning a mouth guard in engagement withthe upper teeth of the subject, the mouth guard comprising a U-shapedelement and a plurality of accelerometers operatively associated withthe U-shaped element, the plurality of accelerometers being spaced fromone another about the U-shaped element; delivering a first impact forceto the helmet, wherein, in response to delivery of the first impactforce, each accelerometer of the plurality of accelerometers of thehelmet is configured to produce an output indicative of the linear andangular acceleration of the helmet and each accelerometer of theplurality of accelerometers of the mouth guard is configured to producean output indicative of the linear and angular acceleration of the mouthguard; transmitting the outputs of the accelerometers of the helmet andthe mouth guard to processing circuitry; determining, through theprocessing circuitry, a transfer function configured to convert theoutputs of the accelerometers of the helmet to the outputs of theaccelerometers of the mouth guard; disengaging the mouth guard from theteeth of the subject; delivering a second impact force to the helmet,wherein, in response to delivery of the second impact force, eachaccelerometer of the plurality of accelerometers of the helmet isconfigured to produce an output indicative of the linear and angularacceleration of the helmet; transmitting the outputs of theaccelerometers of the helmet to the processing circuitry; applying,through the processing circuitry, the transfer function to the outputsof the accelerometers of the helmet to determine the linear and angularacceleration of the head of the subject.
 2. The method of claim 1,wherein the plurality of accelerometers of the mouth guard comprise atleast one accelerometer positioned at a first location about theU-shaped element, at least one accelerometer positioned at a secondlocation about the U-shaped element, and at least one accelerometerpositioned at a third location about the U-shaped element, wherein thefirst, second, and third locations are spaced from one another about anarc defined by the U-shaped element.
 3. The method of claim 2, whereinthe plurality of accelerometers of the mouth guard comprise a firstcluster of at least two accelerometers positioned at the first location,a second cluster of at least two accelerometers positioned at the secondlocation, and a third cluster of at least two accelerometers positionedat the third location, wherein each accelerometer of the plurality ofaccelerometers of the mouth guard is configured to measure linearacceleration in a single axis.
 4. The method of claim 3, wherein atleast one accelerometer of the first, second, and third clusters isconfigured to measure linear acceleration in a first axis, wherein atleast one accelerometer of the first, second, and third clusters isconfigured to measure linear acceleration in a second axis, wherein thefirst axis is perpendicular to the second axis.
 5. The method of claim4, wherein the plurality of accelerometers of the mouth guard aresubstantially co-planar.
 6. The method of claim 5, wherein the mouthguard comprises first, second, and third receptacles coupled to theouter side wall of the mouth guard, wherein the first receptacle isconfigured to receive the first cluster of accelerometers, wherein thesecond receptacle is configured to receive the second cluster ofaccelerometers, and wherein the third receptacle is configured toreceive the third cluster of accelerometers.
 7. The method of claim 2,wherein the plurality of accelerometers of the mouth guard comprise afirst cluster of at least three accelerometers positioned at the firstlocation, a second cluster of at least three accelerometers positionedat the second location, and a third cluster of at least threeaccelerometers positioned at the third location, wherein eachaccelerometer of the plurality of accelerometers of the mouth guard isconfigured to measure linear acceleration in a single axis.
 8. Themethod of claim 7, wherein at least one accelerometer of the first,second, and third clusters is configured to measure linear accelerationin a first axis, wherein at least one accelerometer of the first,second, and third clusters is configured to measure linear accelerationin a second axis, wherein at least one accelerometer of the first,second, and third clusters is configured to measure linear accelerationin a third axis, and wherein the first axis, the second axis, and thethird axis are perpendicular to one another.
 9. The method of claim 2,wherein each accelerometer of the plurality of accelerometers of themouth guard is configured to measure linear acceleration in at least twoperpendicular axes.
 10. The method of claim 2, wherein eachaccelerometer of the plurality of accelerometers of the mouth guard isconfigured to measure linear acceleration in three perpendicular axes.11. The method of claim 2, wherein the U-shaped element defines opposedfirst and second ends, wherein the U-shaped element is substantiallysymmetrical about a central axis, wherein the first location isproximate the first end of the U-shaped element, wherein the secondlocation is proximate the second end of the U-shaped element, andwherein the central axis intersects the third location.